Fuel pump and drive therefor

ABSTRACT

An inlet metering fuel injection pump for pressurizing metered charge of fuel to high pressure is provided with an independent helical gear driven drive shaft having its drive connection with the distributor rotor disposed concentrically with the governor flyweights. The shaft is mounted by a ball bearing received within a deep bearing recess of the housing in which the bearing cannot bottom. The bearing is axially fixed to the shaft and is axially slidable in the bearing recess. A wave washer engages the outer race to bias the shaft toward the distributor rotor to prevent axial oscillations of the shaft and the resultant pumping and pressure pulsations in the fuel which fills the pump housing as torsional loading on the shaft suddenly changes. This eliminates any instability of operation due to to-and-fro flow of fuel past the governor weights and pulsations of pressure acting on the plungers of the charge pump.

United States Patent [191 Donahue Aug. 20, 1974 [5 FUEL PUMP AND DRIVE, THEREFOR [75] Inventor: Kenneth Joseph Donahue, Broad Brook, Conn.

Primary Examiner-William L. Freeh Assistant Examiner-Leonard Smith Attorney, Agent, or FirmPrutzman, Hayes, Kalb & Chilton ABSTRACT An inlet metering fuel injection pump for pressurizing metered charge of fuel to high pressure is provided with an independent helical gear driven drive shaft having its drive connection with the distributor rotor disposed concentrically with the governor flyweights.

The shaft is mounted by a ball bearing received within a deep bearing recess of the housing in which the bearing cannot bottom. The bearing is axially fixed to the shaft and is axially slidable in the bearing recess. A wave washer engages the outer race to bias the shaft toward the distributor rotor to prevent axial oscillations of the shaft and the resultant pumping and pressure pulsations in the fuel which fills the pump housing as torsional loading on the shaft suddenly changes. This eliminates any instability of operation due to toand-fro flow of fuel past the governor weights and pulsations of pressure acting on the plungers of the charge pump.

1 Claim, 1 Drawing Figure 1 FUEL PUMP AND DRIVE THEREFOR The present invention relates to fuel pumps of the type utilized in fuel injection systems for delivering measured charges of liquid fuel to the injectors of a compression-ignition engine. and more particularly to an improved drive for a pump of the type described in US. Letters Pat. No. 3,288,124 issued Nov. 29, I966.

Fuel pumps of the type involved in this invention are mounted by a mounting pad of an associated engine and driven by a drive gear in timed relation with the engine to deliver discrete measured charges of fuel to the several combustion chambers of the engine. The measured charges of fuel are pressurized to high pressure generated intermittently by the pump to produce sudden repetitive changes in torsional loading on the pump drive.

It is customary to use a drive gear having helical gear teeth for increased tooth strength. As a result, varying axial loading is imposed on the drive shaft of the pump suddenly and repetitively which promotes axial oscillations of the drive shaft.

Since the pump housing is filled with liquid fuel, and the axial movement of the shaft changes the volume of the fuel within the housing which is displaced by the shaft, axial shaft oscillations produce a pumping action which produces pulsations in the pressure ofthe fuel within the housing to affect the operation of the pump.

An object of this invention is to provide a pump having an improved drive for overcoming pulsations in housing pressure due to axial shaft oscillations.

Another object of this invention is to maintain the shaft of the pump in a fixed axial position within the housing. A further object is to maintain the drive tang of the shaft in full engagement with the rotor of the pump.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

A better understanding of the invention will be obtained from the following detailed description and the accompanying drawing of an illustrative application of the invention.

In the drawing, the single FIGURE is a fragmentary elevational view, partly broken away, of a fuel pump illustrative of the present invention.

Referring now to the drawing, an illustrative pump is shown as having an external housing or casing provided with an axial bore 12 which rotatably supportsa pump rotor or distributor 14.

At the right end of the housing 10 is mounted a vane type fuel supply or transfer pump 18 driven by the rotor 14 to pressurize incoming fuel from inlet 19 and deliver it through a passage 20 to a metering valve 22. An end plate 24 is biased against the end of the cam ring v26 of the transfer pump 18 by a wave spring washer 30 to maintain the cam ring against a seal ring 32.

A high pressure charge pump generally noted by the numeral 34 is formed by transverse bore 37 in the rotor 14 in which are slidably mounted a pair of opposed plungers 36. The outer end of the plungers 36 engage shoes 38 nesting rollers 40 which are mounted for radial movement in slots formed in the end of the rotor 14. Rotor 14 is provided with a drive slot 42 for receiving the drive tang 44 of a separable gear driven shaft46 aligned with .the bore l2 to provide a driving connection with the rotor. i

Surrounding the rotary member 14 is a generally circular cam ring 48 which encircles the rotor 14 in the plane of revolution of the plungers. The cam conventionally has a plurality of pairs of diametrically'opposed inwardly extending cam lobes 50 which are adapted to actuate the plungers inwardly simultaneously for pressurizing the fuel as the rollers 40 act as cam followers for translating cam contour into reciprocal movement of the plungers 36.

Metered fuel from the metering valve 22 enters the passage 52 of the rotor as the passage 54 registers with metering valve port 56 and passes to the charge pump chamber 58 as the plungers '36 move radially outwardly. The charge of fuel in the charge pump chamber 58 is pressurized as the plungers 36 are actuated inwardly by the cam lobes and is sequentially delivered to the several injectors of the engine as the passage 60 registers, during the rotation of the rotor, with a passage 62 leading to an outlet of the pump for delivery to one of the fuel injectors of the associated engine. As will be apparent, the pressure in the chamber 58 of the charge pump, is suddenly released as the rollers pass over the nose of the cam lobes to suddenly release the loading imposed on the shaft. In addition, the liquid fuel in the pump chamber 58 having been pressurized to several thousand pounds per square inch is compressed and as the rollers pass over the nose of the cam lobes, the pressure is suddenly relieved by the outward movement of the plungers, moving the rollers 40 along the downslope of the cam lobes to produce a reverse driving forceon the shaft 46. In addition, the use of a helical drive gear 64 for the pump, coupled with the sudden release ofthe heavy torsional load as the rollers 40 pass over the nose of the cam lobes, produces a sudden change in the axial thrust load imposed on the shaft 46 to bias it axially.

If the shaft 46 should move to the left, as viewed in the drawing, it displaces less fuel with which the cavity 66 of the'pump is filled to produce a negative pulsation of housing pressure which is maintained at suitable pressure, say, 8 to 10 p.s.i., within the housing. If the shaft 46 moves to the right, its displacement within the pump housing is increased to produce a positive pulsation of pressure within the housing. In addition, if the shaft shifts back and forth axially, the fuel in the gap 68 between the shaft and the rotor rushes in and out to produce a pulsating flow of fuel past the governor weights 70 to introduce an oscillating force, to affect the stability of the governor weights and introduce transients into the control of metering valve 22.

During the outward stroke of the plungers 36, fuel is delivered to the chamber 58 of the charge pump from the metering valve 22 under a pressure depending on the setting of the metering valve which is controlled by the governor in orderto maintain engine speed. Since the outer ends ofthe plungers 36 are subjected to'housing pressure of the fuel within the cavity 66 of the pump, it is apparent that pulsations in the housing pressure will effect the outward movement of the plungers 36and hence the amount of fuel delivered to the chamber 58 of the charge pump. Variations in housing pressureare especially significant under light load, where .the metering valve 22 offers a high restriction to the flow of fuel to the charge pump and a pressure of the metered fuel entering the charge pump chamber 58 is comparatively low. Moreover, any movement of the drive tang 44 of the shaft 46 with respect to the drive tang slot 42 of the rotor produces frictional wear and where the drive tang is not fully engaged with the tang receiving slot 42 increased stress loading is imposed on the bifurcated end of the rotor forming the tang receiving slot.

In accordance with this invention, means are provided for preventing axial oscillations of the drive shaft 46 and to insure that the tang is at all times fully engaged with the tang receiving slot of the rotor despite variations in the build up of manufacturing tolerances in the pump.

As shown in the drawing, the inner race 72 of the ball bearing engages the shaft 46 with a light press fit to fix it rotationally and longitudinally with respect to the shaft. The outer race 74 of the ball bearing is received within a bearing recess 76 of the housing with a sliding fit and the recess 76 is made sufficiently deep to provide an axial gap 78 so that the bearing race 74 does not bottom in the bearing recess 76 regardless of the build up of manufacturing tolerances of the pump. A wave washer 80 engages the end of the outer race 74 to impose a thrust load against the outer race. The wave washer 80 is held in place by a split ring retainer 82 received in a groove 84 in the wall of the bearing recess. The thrust load imposed by the wave washer 80 against the outer bearing race is a fixed, but limited amount, say 12 pounds, which is sufficient to overcome any axial thrust which may be imposed on the rotor shaft during use so that it maintains the tang 44 fully engaged in slot 42 and the end of the rotor 14 bottomed against the end plate 24 of the transfer pump to fix the axial position of the shaft 46 and the rotor 14.

It is apparent that the foregoing drive construction will prevent a pumping action by the shaft and thereby eliminates pulsations of housing pressure in the pump and eliminates the adverse effects of such pulsations on the governor stability and the uniformity of the metering of fuel to the chamber of the charge pump. It is further apparent that the drive construction of this invention maintains the rotor in a fixed axial position to assure uniformity of registry of inlet and outlet ports of the rotor and the mating passages of the housing and to accommodate the build up of manufacturing tolerances inherent in the commercial manufacture of pumps.

As will be apparent to persons skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.

l claim:

I. A fuel injection pump comprising a housing having a bore and a fuel filled cavity, an axially fixed distributor rotor positioned in said bore, a separate drive shaft having an end providing a driving tang received in a mating tang receiving slot in said rotor to provide a driving connection therewith in said cavity, a centrifugal governor having fiyweights in said cavity concentrically of said drive shaft surrounding the end of said shaft, a helical drive gear for said shaft, a bearing mounted by said housing for supporting said shaft, said bearing being axially fixed with respect to said shaft, and means for preventing axial oscillations of said shaft, said means comprising a spring engaging said bearing to bias said shaft toward said rotor to prevent to-and-fro-flow of fuel past said governor flyweights due to pumping oscillations of said shaft and to maintain said tang fully engaged in said tang receiving slot. 

1. A fuel injection pump comprising a housing having a bore and a fuel filled cavity, an axially fixed distributor rotor positioned in said bore, a separate drive shaft having an end providing a driving tang received in a mating tang receiving slot in said rotor to provide a driving connection therewith in said cavity, a centrifugal governor having flyweights in said cavity concentrically of said drive shaft surrounding the end of said shaft, a helical drive gear for said shaft, a bearing mounted by said housing for supporting said shaft, said bearing being axially fixed with respect to said shaft, and means for preventing axial oscillations of said shaft, said means comprising a spring engaging said bearing to bias said shaft toward said rotor to prevent to-and-fro-flow of fuel past said governor flyweights due to pumping oscillations of said shaft and to maintain said tang fully engaged in said tang receiving slot. 